Control circuits for clothes washing and spin-drying machines

ABSTRACT

A control circuit for clothes washing and spin-drying machines incorporating a pulse-producing circuit for generating a series of electric current pulses arranged to be applied to the gate of a thyristor for controlling the power supplied to the drive motor through the thyristor, and speed control means for regulating the pulsed output to give a relatively low-motor speed for washing and a relatively higher motor speed for spin drying, together with switch means operable to control the pulse-producing circuit directly to reduce the conduction angle of the thyristor and hence the power supplied to the motor, for example to zero, and so that the return of the switch means to initial condition causes the motor to be first energized in the low-speed condition, irrespective of the condition of the speedcontrol means, so that restarting the motor at full power is avoided.

United States Patent [72] Inventor Martin Harold Eastall 3,366,861l/l968 Dudler 318/341 Peterborough, England 3,414,791 12/1968 Munson....318/345 [21] Appl. No. 861,716 3,447,055 5/1969 Mason 1. 318/345 [22] SSept 3 9 Primary Examiner-Benjamin Dobeck [45] atmed 2 l 1 AssistantExaminer-Thomas Langer [73] Assrgnee British Domestic Appliances LimitedA0mey Larson Taylor and Hinds Peterborough, England [32] Priority Sept.30, 1968 1 Gram Britain ABSTRACT: A control circuit for clothes washingand spin- 1 ,325/68 drying machines incorporating a pulse-producingcircuit for a generating a series of electric current pulses arranged tobe I t l CONTROL CIRCUITS FOR OTHES ASHING app led to the gate 01'']thyristor for contro llng'the power supplied to the drive motor throughthe thyristor, and speed con AND SHN'DRYI NG MACHINES trol means forregulating the pulsed output to give a relatively sclalmsz Draw'nglow-motor speed for washing and a relatively higher motor [52] us. Cl318/341, speed for pi y g g h i h switch means Operable to 318/327control the pulse-producing circuit directly to reduce the con- [51]Int. Cl H02 5/16 duetien ng of the thyristor n hence h power pp to [50]Field of Search 318/327, the m r x mpl to z r n so that the r rn f h34], 345 switch means to initial condition causes the motor to be firstenergized in the low-speed condition, irrespective of the conl 1 R f r ns Ciied dition of the speedcontrol means, so that restarting the motorUNITED STATES PATENTS at full power is avoided. 3,249,839 5/1966 Fay318/327 AAAA I 6'1 1. 1T3?" 49 -44 47: 44 l 1 g 46 A3 I I {4 5 W 'I 1 1ie I P a m L J T 46 c b III.

PATENTEDuuv 23 ISYI SHEET 1 OF 2 CONTROL CIRCUITS FOR CLOTHES WASHINGAND SPIN-DRYING MACHINES This invention relates to control circuits forclothes washing and spin-drying machines of the kind in which clothescan be washed in a drum by means of a tumbling action effected byrotating the drum at a relatively low speed about a generally horizontalaxis in the presence of a washing liquid and can subsequently be driedby a spinning operation achieved by rotating the drum about the sameaxis at a comparatively high speed and in particular it relates tocontrol circuits for such machines in which both tumbling and spinningoperations are effected by an electric motor operation from an AC supplysource, speed control of the motor to provide the different operationsbeing effected by altering the conduction angle of a thyristor placed inseries with the motor.

A control circuit for a machine of the kind hereinbefore set forth mayinclude a pulse-producing circuit, whose output to a thyristor gate isvariable so as to vary the conduction angle of the thyristor, thuscontrolling the electrical power supplied to the motor, and a feedbackcircuit, sensitive e.g. to motor speed and current, selectivelyconnected to the pulse-producing circuit in such a way that, when soconnected, the control circuit tends to maintain the motor speed at afirst low value, corresponding to the tumbling speed of the clothesdrum, and, when disconnected, the motor is supplied with maximum powerto accelerate the clothes drum to a second higher spinning speed. Thecontrol circuit may also include a program sequence impulse timercontrolling connection between the feedback circuit and thepulse-producing circuit, and a mechanically actuated switch in thesupply circuit to the motor.

A disadvantage of such a control system is that operation of the impulsetimer at intervals, of, say, 2 minutes precludes the fine controlling ofthe duration of spin periods and, in particular, does not allow spinperiods of less than 2 minutes duration as is necessary when processingdelicate fabrics A further disadvantage of this type of control circuitis that in order to effect satisfactory operation of a washing machineusing this type of control circuit it is essential to ensure that thesystem remains energized and hence stabilized, throughout a normalsequence of operations. Thus, for example it is not desireable to switchoff the motor by interrupting the mains supply. Moreover an alternativeswitching operation to deenergize the motor by interrupting an input tothe thyristor, although effective, has the disadvantage that restorationof the supply takes place at full power as the conduction angle set bythe pulse circuit will be at a maximum as soon as the motor comes torest. Restarting of the motor at full power inflicts a severe shock loadon the washing machine transmission.

An object of the present invention is to provide a control circuit inwhich these disadvantages are substantially avoided.

According to the present invention in a control circuit for a clotheswashing and spin drying machine of the kind hereinbefore set forth, andin which the electric motor is preferably a series wound commutator typeelectric driving motor, there is provided a first, pulse-producingcircuit for generating a series of electric current pulses arranged tobe applied to the gate of a thyristor for controlling the conductionangle thereof and hence the power supplied to the motor through thethyristor, a second, feedback circuit for regulating the pulsed outputfrom the control circuit to the thyristor so as to tend to maintain themotor speed at a first, low (washing) speed, and a third, speed controlcircuit for selectively overriding the feedback circuit so as to tend toincrease the motor speed to a second and higher (spin drying) speed,which circuit includes switch means connected to the input of thepulse-producing circuit and operable to control directly thepulse-producing circuit, irrespective of the condition of the feedbackand speed control circuits, so as to reduce significantly the conductionangle of the thyristor and hence the power supplied to the motor.

The switch means may, for example, be operable to reduce the conductionangle of the thyristor, and hence the motor speed, to zero. With such anarrangement the return of the switch means to the initial, unoperated,condition will cause the motor to be first energized in the low speedcondition, and restarting of the motor at full power is thus avoided. Inaddition control of the motor is achieved independently of the impulsetimer.

In one convenient form of the invention, the switch means comprises asolid state switching circuit connected to the input of the pulseproducing circuit and operable to alter the output from thepulse-producing circuit in such a manner as to reduce the conductionangle of the thyristor and hence the motor power input to zero, theenergization required for actuation of the solid state switching devicebeing derived from a resistance-capacitance delay line energizedsimultaneously with a change in motor speed, from low speed to highspeed operation under the control of the speed control circuit, the timedelay of the resistance capacitance circuit being so selected as tocause deenergization of the motor at a predetermined time after thechangeover from low speed to high speed.

The solid state switching circuit may include at least one solid stateswitching device, such as a transistor, which is normally nonconductingbut is rendered conducting by said resistance capacitance delay lineafter a predetermined time interval following the changeover from lowspeed to high speed, the pulse producing circuit being responsive to thechange in state of the device to the conductive condition to reduce theconduction angle of the thyristor to zero.

Alternatively the switching circuit might include a switching devicewhich is normally conducting but is arranged to be renderednonconducting by said resistance capacitance delay line, thepulse-producing circuit being responsive to the change in state of thedevice to the nonconducting condition to reduce the conduction angle ofthe thyristor to zero.

In another convenient form of the invention, mechanically actuatedswitching means are connected so as to control an input to thepulse-producing circuit such that when the switching means is closed thedrive motor is deenergized, and that when the switch is subsequentlyopened the output from the pulse circuit increases the conduction angleof the thyristor gradually from zero, smoothly accelerating the motorfrom rest to a running speed.

Alternatively it can be arranged for the pulse-producing circuit to bedeenergized when an associated switch is open, the subsequent closure ofthe switch causing the output of pulseproducing circuit to increase theconduction angle of the thyristor to increase gradually from zero, so asto smoothly accelerate the motor from rest.

In order that the invention may be more clearly understood, two diflerent embodiments of it as applied to the control of the motor of awashing machine will now be described by way of example with referenceto FIGS. 1 and 2 of the accompanying drawings which represent circuitdiagrams of the two control circuits.

The machine, which is not itself illustrated in either Figure of thedrawings, typically comprises a drum mounted on a shaft in bearings soas to be rotatable on a horizontal axis within a liquid containingcylinder, which is suspended by means of cooperating springs and damperswithin an outer cabinet. A series-wound electric drive motor is carriedby the liquid containing cylinder and is drivingly connected by means ofa VV or multi-V belt drive system to a pulley wheel secured to the drumshaft outside the liquid containing cylinder, The system is such thatthe drum is rotated at a speed below the motor speed and in a fixedrelationship of say l:l0 or thereabouts. Liquid is supplied to thecylinder through an electromagnetically actuated inlet valve and removedby an electric motor driven pump. An electric tubular sheathed wireheating element is mounted in thecylinder for heating the wash liquid.

The various functions of the washing machine are sequentially controlledby a program controller comprising a asynchronous electric timer motoractuating, via a stepping linkage, a number of switch operating earnsthe switches controlling the supply of electrical power to the variousparts of the machine in sequence so as to cause a particular program ofoperations to be performed on clothes placed in the drum and a solidstate switching circuit, also controlled by the timer motor for thedrive motor of the machine.

With reference now to FIG. 1. which shows the first control circuit forthe washing machine, the drum of the washing machine (not shown) isrotatably driven by a series wound electric motor 1. The machine isconnected to a source of AC supply through a main isolating switch. (notshown) the motor being supplied through a thyristor 2 and a low valueresistor 3. A diode 4 connected in parallel with the motor acts as aflywheel diode in known manner to provide a smoothing effect on themotor current supply.

The thyristor 2 is fired by a pulse producing circuit (indicated bychain dotted lines A) whose output (to the thyristor) is controlled by anegative feedback circuit B, sensitive to rising motor speed, a positivefeedback circuit 13 sensitive to rising motor current. a speed controlswitch C and a solid state relay circuit D. these control circuitsacting to regulate the pulses produced by circuit A. and hence thepulses of DC power supplied to the motor from the thyristor.

The speed control switch C is actuated. when required, by means of a camin the program controller driven by a synchronous motor 6. The motor 6also determines the condition of other cam actuated switches 7 and 8 inthe electrical supply to a heater 9 and a pump motor 10 respectively. Aswitch 41 is also controlled by a cam. actuated by the programcontroller. this switch, when closed. cuts off the supply of power tothe :motor irrespective of the conditions existing at the time in thecontrol circuits B. C and D. The function of this switch will be morefully described hereinafter.

A further cam-actuated changeover switch 29 is arranged to reverseposition at regular intervals through the washing action in order toperiodically reverse the drive motor. and hence the wash drum. and thusprovide a tumbling action on the clothes within the drum. The switch 41is closed momentarily at each reversal to cut off the motor power andprevent arcing in switch 29.

In operation of the washing machine its various functions aresequentially controlled by the program controller which may be set toselect one of several washing sequences to suit the clothes beingprocessed. A complete washing and drying cycle may, for example.comprise the following steps:

Prewash. spin. wash. spin. rinse and spin.

During the prewash. wash and rinse functions the drum is rotated at lowspeeds (say 50 rev./min.) in one direction for a short period of time(say seconds) and then rotated in the opposite direction for an equalperiod of time. Since the speed of rotation during these operations islow. the centrifugal force on the clothes is not sufficient to hold themin contact with the wall of the drum as they are carried round and as aresult they tumble within the drum.

The spin action is achieved by rotating the drum at a high speed (say1.000 rev./min.) in one direction only, the centrifugal force on theclothes being sufficiently large to retain them in contact with the wallof the drum and to extract any contained liquid from them.

The low speed of rotation of the drum is determined by the pulseproducing circuit A and the feedback circuits B and E the switch C beingopen at this time. Thus, the circuits A. B and B are set so as tomaintain the motor speed at substantially 500 rev./min., correspondingto a drum speed of 50 rev./min. irrespective of normal variations inload on the motor.

The pulse producing circuit A comprises. essentially. a capacitor 12transistors 13 and 14 and a zener diode 15 all supplied with low voltageDC by means ofa voltage dropping resistor 61 and a zener diode 17 andarranged so that the circuit is supplied with a pulse of approximatelyrectangular form during each positive half cycle of the AC supply. thenegative half-cycle being suppressed by the zener diode 17. During eachhalf-cycle the capacitor 12 becomes charged through the transistor 14which is conductive at this time due to the voltage at its emitter beingbelow that at its base (this base voltage being supplied by potentialdividing resistors 33 and 34) but being below the voltage of the zenerdiode 15. When the voltage across this capacitor becomes large enough.the base current in transistor 13 turns on the transistor. Thetransistor 13 then supplies base current to transistor 14. turning it onso as to supply more base current to transistor 13. This cumulativeaction leads to rapid saturation of these transistors with the resultthat the voltage of the zener diode 15 is exceeded and a furthercapacitor 32 discharges through the saturated transistors into the gateof the thyristor 2. As a result the thyristor switches on. supplying themotor with a pulse of DC power.

Regulations of the pulses applied to the thyristor for controlling theconduction angle thereof is effected by varying the voltage at the baseof the transistor 19. As this voltage rises. the rate of charge of thecapacitor 12 decreases with the result that the firing pulse to the gateof the thyristor is delayed until later in the halfcycle and theconduction angle of the supply to the drive motor is thereby decreased.

The voltage at the base of the transistor 19 is controlled by thefeedback circuits B and B The negative feedback circuits B comprises atachogenerator 18 (connected to the driving motor 1) which applies avoltage. increasing with motor speed. to the base of the transistor 19.As the voltage applied to the base of transistor 19 increases, the powersupplied to the motor, and hence the motor speed. decreases. The inputof this negative feedback circuit B is supplied from a reference voltagedetermined by the output voltage of the positive feedback circuit B Thecircuit B 'comprises resistors 3 and 20 and a capacitor 21, thearrangement being such that as the motor load. and hence the currentrequired. increases. the potential across the resistor 3 will increasecausing the reference voltage at the input to circuit l3 with respect tothe common rail to decrease and hence the control voltage to thetransistor 19 to decrease so that the power input to the motor increasesto maintain the motor speed.

A preset variable resistor 22 controls the gain of the transistor pair19 and 14 hence the response of the pulse circuit A to the feedbackcircuits B and E the value being selected so as to maintain the motorspeed at 500 rev./min. at this time.

AT the end ofa washing (or rinsing) period the timer motor 6 closes theswitch 8 so as to energize the electric motor driven pump 10 to removeall the free washing liquid from the machine. Simultaneously the timercloses the switch C to cause the motor to accelerate to a high speed toprovide a higher spinning speed for the clothes drum. Thus. closure ofthe switch C reduces the reference voltage applied at the input of thetachogenerator and hence the voltage applied to the base of thetransistor 19 to zero. As a result of this the conduction angle set bythe pulses from the pulse-producing circuit to the thyristor increasesto the maximum possible value and the motor speed rises rapidly.Simultaneously (with the closure of the switch C) the voltage applied toa zener diode 42 in the spin timer circuit D is reduced. thus increasingthe voltage across it and causing it to conduct. A switching transistor43 is switched off at this time by virtue ofa biasing voltage betweenits emitter and base due to a potential dividing circuit comprisingresistors 47 and 48 and the uncharged capacitor 44. respectively. Assoon as a conductive path is established through the zener diode thecapacitor 44 commences to charge through a resistor 45 and the zenerdiode 42. a diode 46 being provided to prevent the capacitor dischargingduring alternate cycles of the supply. The base potential at transistor43 thus decreases as the charge in capacitor 43 rises until. at a fixedtime thereafter. it is below the bias potential present at the emitterof this transistor. When this change occurs the emitter base junction ofthe transistor becomes forwardly biassed. i.e. turned on. with theresult that it becomes highly conductive between its collector and itsemitter so that the voltage applied to the base of transistor 19 israised substantially to switch this transistor hard on and entirelysuppress the production of pulses from the circuit A to the thyristor 2,by

turning the transistor 14 off, with the result that the drive motor isdeenergized, and remains in this condition until the switch C is againopened by timer motor 6. The charging rate of capacitor 44 is selectedto provide the required spin duration.

When the switch C is opened, the voltage across the zener diode 42decreases so that the zener reverts to its nonconduct ing condition. Thecapacitor is now able to discharge through a high value resistor 49. Thetransistor 43 switches off as the voltage at its base rises above thatat its emitter and thus the base voltage of transistor 19 decreases to avalue determined by the output from the feedback circuits B and B thisoutput corresponding to the maximum power requirement for the motor. Thepulse circuit, when reenergized in this way through transistor 19,produces and feeds to the thyristor pulses of rapidly increasingconduction angle such that the motor smoothly accelerates from rest tothe desired running speed, in this case 500 rev./min., whereupon theincreasing input voltage generated by the feedback circuits and suppliedto the base of transistor 19 prevents any further motor speed increase.

It is convenient to provide a second mechanically actuated switch 41 inparallel with the transistor switch 43 and actuated by the program timersuch that closure of this switch turns the transistor 19 hard on tosuppress the production of pulses from the circuit A so as to deenergizethe motor at whichever point in the program may be desirable, e.g.between motor reversals during a washing operation. In this way shockloads on the machine transmission are reduced and the subsequentrestarting of the motor on opening the switch 41 occurs as set outpreviously.

it should be appreciated that, although in this embodiment the controlcircuit provides a spinning operation of fixed duration, the inventionis equally applicable to a circuit in which the duration of the spinningoperation is adjustable by e.g. varying the values of the capacitor 44or the resistor 45.

It will also be appreciated that the invention is applicable to otherforms of circuit arrangements incorporating a pulseproducing circuit forgenerating a series of electric pulses applied to the thyristor forvarying the conduction angle of the latter and hence the power suppliedto the motor, together with a feedback circuit for maintaining the motorspeed at a first low washing speed, and speed control means forselectively overriding the feedback circuit so as to tend to increasethe motor speed to a higher spin drying speed.

Thus referring now to FIG. 2, which illustrates the second embodiment ofthe invention, the washing machine motor 1 is similarly supplied withpower through a thyristor 2 and resistor 3, and the conduction angle ofthe thyristor is controlled by a pulse producing circuit A which iscontrolled in turn by a negative feedback circuit B sensitive to risingmotor speed, and a positive feedback circuit B, sensitive to risingmotor current, these circuits acting to maintain the motor speed atsubstantially 500 rev/min. for washing and rinsing, and the operation ofthe machine and its various functions being similarly controlled by aprogram controller capable of being set to select one of an appropriatenumber of washing sequences. Overriding of the feedback circuits toaccelerate the motor 1 tea spin-drying speed is achieved by a solidstate time dependent circuit E as will be subsequently described.

In this embodiment the circuits A, B,, B are supplied with low voltageDC by means of a voltage dropping resistance 61, a diode 40 a smoothingcapacitor 60 and a zener diode 17.

The pulse producing circuit A comprises, essentially a capacitor 12, acomplementary pair of transistors 13 and 14, a further transistor 19 anda differentiating circuit comprising resistor 53 and a further capacitor54. In use the differentiating circuit is supplied with a voltage ofapproximately square wave form. During each positive half-cycle of thesquare wave the capacitor 12 becomes charged via diode 55 at a ratedependent upon the voltage applied to the base of the transistor 19 andthe value of the resistor 52, the transistor 19 being conductive at thistime, due to the voltage at its emitter being below that at its base,this base voltage being normally made up of an adjustable referencevoltage derived from a poten' tiometer network P and modified by the twofeed back circuits B, and 8,, as will subsequently be described.

When the voltage across the capacitor 12 becomes large enough, this willcause the transistor 13 to conduct. The transistor 13 then supplies basecurrent to transistor 14 turning it on so as to supply more base currentto transistor 13. This cumulative action leads to rapid saturation ofthese transistors with the result that the lower end of capacitor 12 iseffectively connected to the H.T. rail via transistors 13 and 14,resulting in a voltage pulse which is now positive with respect to theH.T. rail being applied to the gate of the thyristor 2. Diode 55 nowprevents capacitor 12 from short circuiting directly through transistors13 and 14 and as a result'the thyristor switches on, supplying the motorwith a pulse of DC power.

Control of the conduction angle of the motor current wave form iseffected by varying the rate at which capacitor 12 charges which is inturn affected by varying the voltage at the base of the transistor 19.As this voltage rises the rate of charge of the capacitor 12 increases,with the result that the firing pulse to the gate of the thyristor isapplied earlier in the half-cycle with the result that the conductionangle of the supply to the drive motor is increased giving a fastermotor speed.

Similarly if the rate of the charge of the capacitor 12 decreases as aresult of the base voltage of the transistor 19 being reduced the firingpulse to the gate of the thyristor is applied later in the half-cyclecausing the conduction angle of the supply to the drive motor beingdecreased and reducing the motor speed.

As previously pointed out the voltage at the base of the transistor 19is controlled by the feedback circuits B and B The negative feedbackcircuits 8 comprises a tachogenerator l8 (mechanically connected to thedriving motor 1 which applies a voltage, decreasing with increasingmotor speed, to the base of a transistor 19. As the voltage applied tothe base of transistor 19 decreases the power supplied to the motor andhence the motor speed decreases.

The positive feedback circuit B comprises resistors 3, 20 and 21 anddiode 56, the arrangement being such that as the motor load, and hencethe current required for the motor, increases, the positive feedbackvoltage applied to the base of the transistor 19 also increases so thatthe power input to the motor increases to maintain the motor speed.

Tl'le feedback circuits B, and B and the value of the reference voltageare chosen so as to maintain the motor speed at approximately 500rev./min. at this time i.e. with circuit E isolated.

At the end of a washing (or rinsing) period the timer motor 6 closes theswitch 8 so as to energize the electric motor driven pump It) to removeall the free washing liquid from the machine. Simultaneously the timeropens switch 5 which controls the time dependent circuit E. When switch5 is opened a capacitor 24, (suitably 250 microfarads) commences todischarge through a high value adjustable resistor 25 (suitably 0 to 300K). As a result the voltage at the base of the transistor 11 increasesslowly over a period of time (which can be determined by adjustment ofthe high value resistor 25) and may for example be on the order of 30seconds. The transistor 1 l is then switched on and thereafter the-'current through the transistor (from collector to emitter) increasesslowly thus increasing the control voltage applied at the base oftransistor 19 overriding the feedback circuits so that the motor speed,and hence the drum speed, slowly increases.

During this slow acceleration from washing speed the centrifugal forceon the clothes gradually increases until exceeds the gravitational forceon the clothes. This gradual increase in speed has the effect of slowlymoving the clothes outward to contact the wall of the drum in a balancedmanner.

As a transistor 11 becomes more conductive the voltage at the base of afurther transistor 27 rises this causing the transistor 19 to riserapidly to a maximum determined by the transistor 27 reaching a stableconducting condition.

As this base current further increases the transistor 19 turns on hardermore rapidly, the conduction angle of the rectified supply to the motorsimilarly increasing rapidly to its maximum, and the motor is suppliedwith maximum power and rapidly accelerates the clothes drum to high spindrying speed. The capacitor and resistor values can readily be selected,in dependence upon the transistors employed, to obtain the appropriatetime intervals.

During the slow acceleration period and with the switch SS closed acapacito'r 31 charges up via a resistor 50 and diode 51, When transistor27 breaks over the voltage at its collector decreases and diode 51 isnow reverse biassed thus preventing further charge to capacitor 31(suitably 250 microfarads). Capacitor 31 now discharges via variableresistor 57 (suitably to 300 K) over a period of time (e.g. l seconds)preset by the variable resistor 57.

As capacitor 31 discharges the voltage at the junction of diode 51capacitor 31 and variable resistor 57 decreases and a point is reachedwhen transistor 33 turns off. The voltage at the collector of transistor33 increases and since this is connected to the base of the transistor13 in the pulse producing circuit A the latter will be prevented fromfiring and hence will prevent the application ofa firing pulse to thethyristor 2, thus terminating the spinning operation.

If the switch SS is opened prior to the commencement ofthe sequence ofoperations capacitor 31 is prevented from charging and the drum willcontinue to be driven at spin drying speed. The spinning operation'mayin such a case be terminated by closure of a further switch whichreduces the voltage at the base of the transistor 19 to a value suchthat it switches off, thereby suppressing the pulses and reducing theconduction angle of the thyristor 2 to zero. This closure of the switchS can be arranged to take place under the control of the timer to give alonger spin drying time than is provided for the charging of thecapacitor 31.

lclaim:

l. A control arrangement for an automatic clothes washing and spindrying machine of the kind designed to carry out a programmed sequenceof operations and incorporating a drum rotatable about a horizontalaxis, said arrangement comprising an electric motor for driving the drumenergizable from an alternating current supply through a thyristor, anda control circuit for altering the conduction angle of the thyristor tocause the motor to rotate at a relatively low speed for washing and acomparatively high speed for spin drying, said control circuitcomprising a first, pulse-producing circuit for applying a series ofelectric current pulses for application to the gate of the thyristor tocontrol the conduction angle thereof and hence control the powersupplied to the motor through the thyristor, a second, feedback circuitfor regulating the output from the control circuit so as to tend tomaintain the motor speed at a first, low speed, and a third, speedcontrol circuit for selectively overriding the feedback circuit so as totend to increase the motor speed to a second and higher speed, thecontrol circuit further including switch means connected to an input ofthe pulse-producing circuit for directly controlling the pulse-producingcircuit, said switch means, when operable, overriding the feedback andspeed-control circuits such that the conduction angle of the thyristor,and hence the power supplied to the motor, is significantly reduced andcausing, upon subsequent return to the initial state thereof, a gradualincrease in the conduction angle of the thyristor from the reduced valueto a value determined by the feedback and speed-control circuits.

2. A control arrangement according to claim 1, wherein the switch meanscomprises a solid state switching circuit connected to the input of theulse roducing circuit and operable to alter the output from t e puse-producmg circuit in such a manner as to reduce the conduction angleof the thyristor and hence the motor power input to zero.

3. A control arrangement according to claim 2, wherein the energizationrequired for actuation of the solid state switching device is derivedfrom a resistance-capacitance delay line energized simultaneously with achange in motor speed from low speed to high speed operation under thecontrol of the speed control circuit, the time delay of the resistancecapacitance circuit being so selected as to cause deenergization of themotor at a predetermined time after the changeover from low speed tohigh speed.

4. A control arrangement according to claim 3, wherein the solid stateswitching circuit includes at least one solid state switching device,which is normally nonconducting but is rendered conducting by saidresistance capacitance delay line after a predetermined time intervalfollowing the changeover from low speed to high speed, the pulseproducing circuit being responsive to the change in state of the deviceto the conductive condition to reduce the conduction angle of thethyristor to zero.

5. A control arrangement according to claim 3, wherein the solid stateswitching circuit includes a solid state switching device which isnormally conducting but is arranged to be rendered nonconducting by saidresistance capacitance delay line after a predetermined time intervalfollowing the changeover from low speed to high speed, thepulse-producing circuit being responsive to the change in state of thedevice to the nonconducting condition to reduce the conduction angle ofthe thyristor to zero.

6. A control arrangement according to claim I, wherein the switchingmeans comprises a mechanically actuated switch connected so as tocontrol an input to the pulse-producing circuit such that when theswitching means is closed the drive motor is deenergized, and that whenthe switch is subsequently opened the output from the pulse circuitincreases the conduction angle of the thyristor gradually from zero,smoothly accelerating the motor from rest to a running speed.

7. A control arrangement according to claim I wherein the switchingmeans comprises a mechanically actuated switch connected to the input ofthe pulse-producing circuit so that when the switch is open the drivemotor is deenergized, but such that when the switch is subsequentlyclosed the output from the pulse circuit increases the conduction angleof the thyristor gradually from zero, smoothly accelerating the motorfrom rest to a running speed.

8. A control arrangement according to claim 1, wherein thepulse-producing circuit includes a capacitor, means for charging thecapacitor during appropriate half-cycles of the supply voltage at a ratedependent upon feedback and speed control circuits, and means responsiveto the charge on the capacitor for generating a pulse when the charge onthe capacitor reaches a predetermined value, the rate of charge of thecapacitor being determined by the degree of conductivity of atransistor, and the said switch means being operable to change theconductivity of the transistor by an amount sufficient to suppress thepulses and hence reduce the power supplied to the motor to zero.

1. A control arrangement for an automatic clothes washing and spindrying machine of the kind designed to carry out a programmed sequenceof operations and incorporating a drum rotatable about a horizontalaxis, said arrangement comprising an electric motor for driving the drumenergizable from an alternating current supply through a thyristor, anda control circuit for altering the conduction angle of the thyristor tocause the motor to rotate at a relatively low speed for washing and acomparatively high speed for spin drying, said control circuitcomprising a first, pulse-producing circuit for applying a series ofelectric current pulses for application to the gate of the thyristor tocontrol the conduction angle thereof and hence control the powersupplied to the motor through the thyristor, a second, feedback circuitfor regulating the output from the control circuit so as to tend tomaintain the motor speed at a first, low speed, and a third, speedcontrol circuit for selectively overriding the feedback circuit so as totend to increase the motor speed to a second and higher speed, thecontrol circuit further including switch means connected to an input ofthe pulse-producing circuit for directly controlling the pulse-producingcircuit, said switch means, when operable, overriding the feedback andspeed-control circuits such that the conduction angle of the thyristor,and hence the power supplied to the motor, is significantly reduced andcausing, upon subsequent return to the initial state thereof, a gradualincrease in the conduction angle of the thyristor from the reduced valueto a value determined by the feedback and speedcontrol circuits.
 2. Acontrol arrangement according to claim 1, wherein the switch meanscomprises a solid state switching circuit connected to the input of thepulse producing circuit and operable to alter the output from thepulse-producing circuit in such a manner as to reduce the conductionangle of the thyristor and hence the motor power input to zero.
 3. Acontrol arrangement according to claim 2, wherein the energizationrequired for actuation of the solid state switching device is derivedfrom a resistance-capacitance delay line energized simultaneously with achange in motor speed from low speed to high speed operation under thecontrol of the speed control circuit, the time delay oF the resistancecapacitance circuit being so selected as to cause deenergization of themotor at a predetermined time after the changeover from low speed tohigh speed.
 4. A control arrangement according to claim 3, wherein thesolid state switching circuit includes at least one solid stateswitching device, which is normally nonconducting but is renderedconducting by said resistance capacitance delay line after apredetermined time interval following the changeover from low speed tohigh speed, the pulse producing circuit being responsive to the changein state of the device to the conductive condition to reduce theconduction angle of the thyristor to zero.
 5. A control arrangementaccording to claim 3, wherein the solid state switching circuit includesa solid state switching device which is normally conducting but isarranged to be rendered nonconducting by said resistance capacitancedelay line after a predetermined time interval following the changeoverfrom low speed to high speed, the pulse-producing circuit beingresponsive to the change in state of the device to the nonconductingcondition to reduce the conduction angle of the thyristor to zero.
 6. Acontrol arrangement according to claim 1, wherein the switching meanscomprises a mechanically actuated switch connected so as to control aninput to the pulse-producing circuit such that when the switching meansis closed the drive motor is deenergized, and that when the switch issubsequently opened the output from the pulse circuit increases theconduction angle of the thyristor gradually from zero, smoothlyaccelerating the motor from rest to a running speed.
 7. A controlarrangement according to claim 1 wherein the switching means comprises amechanically actuated switch connected to the input of thepulse-producing circuit so that when the switch is open the drive motoris deenergized, but such that when the switch is subsequently closed theoutput from the pulse circuit increases the conduction angle of thethyristor gradually from zero, smoothly accelerating the motor from restto a running speed.
 8. A control arrangement according to claim 1,wherein the pulse-producing circuit includes a capacitor, means forcharging the capacitor during appropriate half-cycles of the supplyvoltage at a rate dependent upon feedback and speed control circuits,and means responsive to the charge on the capacitor for generating apulse when the charge on the capacitor reaches a predetermined value,the rate of charge of the capacitor being determined by the degree ofconductivity of a transistor, and the said switch means being operableto change the conductivity of the transistor by an amount sufficient tosuppress the pulses and hence reduce the power supplied to the motor tozero.